1. Field of the Invention
The present invention relates generally to optical fiber, and more particularly to coating systems for optical fiber and coated optical fibers.
2. Technical Background
Optical fiber has acquired an increasingly important role in the field of telecommunications, frequently replacing existing copper wires. This trend has had a significant impact in all areas of telecommunications, greatly increasing the amount of data that is transmitted. Further increase in the use of optical fiber is foreseen, especially in metro and fiber-to-the-home applications, as local fiber networks are pushed to deliver an ever-increasing volume of audio, video, and data signals to residential and commercial customers. In addition, use of fiber in home and commercial premise networks for internal data, audio, and video communications has begun, and is expected to increase.
Optical fiber is typically made of glass, and usually has a polymeric primary coating and a polymeric secondary coating. The primary coating (also known as an inner primary coating), is typically applied directly to the glass fiber, and when cured forms a soft, elastic, compliant material encapsulating the glass fiber. The primary coating has a low Young's modulus, and serves as a buffer to cushion and protect the glass fiber during bending, cabling or spooling. The secondary coating (also known as an outer primary coating) is applied over the primary coating, and acts as a tough, protective outer layer that prevents damage to the glass fiber during processing, handling and use.
It is commonly believed that water can corrode glass and introduce defects onto a glass surface. In order to protect the glass surface of the optical fiber from water, conventional optical fiber primary coatings are designed to be hydrophobic in nature. While highly hydrophobic primary coatings do provide a low-water environment to the optical fiber, they are also quite sensitive to hydrocarbon solvents as well as to the hydrophobic fill compounds commonly used in optical fiber cables. Primary coatings of more moderate hydrophobicity are less sensitive to cable fill compounds, may exhibit water bubble formation (e.g., a “mist” of very fine bubbles) when soaked in water. There remains a need for an optical fiber coating system having a primary coating having desirable mechanical properties and that is resistant to hydrophobic solvents and cable fill compounds as well as to the formation of water bubbles when the optical fiber is soaked in water.